In a typical slurry polymerization system, monomer (and possibly co-monomer, liquid diluents, and catalyst) are fed into a continuously stirred reactor. The monomer (and possibly co-monomer) reacts to produce a product effluent containing solid polymer particles of various sizes, liquid diluents (if used), unreacted monomer, and catalyst. The effluent, is removed from the reactor, and typically contains between about 40 to 60 wt % unreacted monomer and/or diluents. For economical operation of this process the unreacted monomer and/or diluents are separated from the polymer solids and then returned to the reactor(s).
U.S. Publication No. 2005/0095176 is hereby incorporated by reference in full. U.S. Publication No. 2005/0095176 describes a conventional method of separating polymer solids from unreacted monomer by first vaporizing at least a portion of the reactor effluent. The withdrawn slurry is passed into a high-pressure flash chamber. After leaving the high-pressure flash chamber, the monomer stream is condensed using a simple heat exchange condenser and recycled into the reactor. However, in this conventional method the monomer stream contains a relatively large amount of residual solid particles. These residual solid particles may contain catalyst that will cause further polymerization and could foul the system.
EP 0100550 is hereby incorporated by reference in full. EP 0100550 describes an alternative conventional method of separating olefin solids from unreacted monomer by first vaporizing at least a portion of the reactor effluent. The solids are removed from the unreacted monomer by passing the reactor effluent through a series of bag filters. The unreacted monomer stream is relatively free of residual particles, however, because of the relatively low operating pressure of the filters the unreacted monomer stream must undergo compression before it can be recycled. Compressors are undesirable in this process as they have relatively high capital expense and operating costs.
Accordingly, there is a need for a process that can separate unreacted monomer from an effluent stream into a relatively pure stream, and does not require compression.